Rotary drum mixer



Dec. 6, 1955 P. HOWDEN ROTARY DRUM MIXER 2 Sheets-Sheet 1 Filed May 29,1953 F/GZ Inventor r22; r flmm/ y 21w v mm A ft0rney 6, 55 P. HOWDEN2,726,068

ROTARY DRUM MIXER Filed May 29, 1953 2 Sheets-Sheet 2 lllllllllllllllllUlll llllllllllllllllllll ll lllllll B II I Inventor 7 W ByWM 5 M Zdz fi Attorney 2,726,068 Ice Patented Dec. 6, 1955 ROTARY DRUMMIXER Peter Howden, Misterton, England, assignor to Ernest Nowell &Company Limited, Misterton, England Application May 29, 1953, Serial No.358,340 Claims priority, application Great Britain August 2, 1952Claims. (Cl. 259-13) This invention relates to rotary drum mixers formixing powdered and granular materials, with or Without liquids.

The horizontal rotary drum mixer is particularly suitable for highthroughput e. g., for mixing iron ore, coke, etc., but is not itselfadapted to blend materials fed into it in large individual batches.Improved blending is obtained by the use of an independently drivenscroll or paddle shaft arranged lengthwise of the interior of the drumwithin the position occupied by the material as it it lifted up one sideof the drum by the rotation. The paddles of the scroll are set at anangle to propel the material lengthwise, but their tips lie clear of thedrum to allow some of the material to be carried up close to the shellby the rotation of the drum without being affected by the paddles. Thislifted material cascades at a height approximately that of thehorizontal centre line of the drum as gravity overcomes the frictionwith the shell, and the material falls on to the bed of material thathas been projected forward by the paddles. The relative longitudinalmovement that takes place between the part of the material projected bythe paddles and the part that is cascaded produces a blending, andopposes the tendency for successive batches of the materials .to beincompletely mixed by passing through the drum still as batches with themixing resulting from the turning over in cascading mainly confined towhere one batch adjoins another.

For some purposes, however, still better blending is desired, and theobject of the invention is to provide a mixer of this drum and scrolltype capable of giving im proved blending.

According to the present invention, a horizontal rotary drum mixercomprises a drum provided with two or more scrolls or paddle shafts(hereafter referred to as scrolls) disposed longitudinally of the drumwithin the position occupied during rotation of the drum by the materialto be mixed, with means for rotating the scrolls at different speedswith respect to each other. Since the rotation of the drum lifts thematerial up one side of the drum to a height from which it repeatedlycascades, the scroll shafts occupy appropriately different heightsinside the drum. Thus, with two scrolls, the lower scroll shaft ispreferably somewhat offset from the vertical centre line of the drum inthe direction of rotation of the drum, and the upper scroll shaft ismuch further offset, to lie somewhat below the horizontal centre line ofthe drum. Conveniently, the two shafts may lie at the same radialdistance from the axis of the drum. In the case of both scrolls, thereis clearance between the tips of the paddles and the inside of the drumshell, With paddles of the same radius on shafts at the same radius fromthe drum axis, each scroll provides the same clearance be tween itspaddles and the shell.

The radius of the paddles is such that the scrolls will be wholly orsubstantially immersed in the material being mixed, with the materialamounting to say one-third of the volume of the drum.

The tip speed of a scroll is substantially in excess of the peripheralspeed of the shell, e. g. 5 to 20 times as great. The direction ofrotation should be in the same direction as that of the drum, to assistboth the lifting and the cascading of the material.

With the scrolls driven at different speeds with respect to each other,material propelled longitudinally by one scroll reaches a lengthwiseposition different from that propelled by the other scroll, so that ofthe material subjected to direct propelling action by the scrolls thereis repeated mixing as the material progresses from end to end of thedrum. In addition, material lifted by the drum from the neighbourhood ofthe lower scroll and carried through the clearance between the shell andthe paddles cascades on to the more elevated scroll and is mixed by thatscroll with material in which that scroll is rotating, to effect furtherblending. Consequently, at any position in the length of the drum, partof the material is being moved lengthwise at different speeds by thescrolls, and this, with the further blending of the cascaded material,strongly opposes any tendency of the material to progress through thedrum as incompletely mixed batches. cessive charges of material are thuswell mixed before they reach the discharge end of the drum.

By way of example, one construction of two-scroll mixer according to theinvention will now be described in greater detail with reference to theaccompanying drawings, in which Figure l is a side elevation, largely insection;

Figure 2 is a section on the line 2-2 of Figure 1;

Figure 3 is a plan; and

Figure 4 is an end elevation corresponding to Figure 2.

The drum 1 is provided with the usual tyres 2 resting on rollers 3 andguided by rollers 4. It is closed at one end by a stationary plate 5incorporating a feed chute 6, and projects at the other end into adischarge chute 7, from which the mixed material drops, for removal byconveyor belt or otherwise, any steam, water vapour, or gas beingexhausted upwardly. The drum is driven by a motor 3 through worm gearing9 and a toothed girth ring 10.

Two scroll shafts ll, 12 of square section inside the drum, pass throughsealing plates 13, 14 in the closing plate 5 and in the far side of thechute 7, to be carried by bearing housings l5, 16 at positions inrelation to the cross-section of the drum 1 clearly shown in Figure 2.With the drum rotatable clockwise in that figure, the lower shaft 11 isoffset to the left of the vertical centre line 17, and the upper shaftlies somewhat below the horizontal centre line 18 and is substantiallyoffset to the left of the vertical centre line, so that both lieimmersed in the material 19 that is lifted up the left-hand side of thedrum to a height somewhat above the line 18 before it cascades towardsthe bottom of the drum.

Each face of the square section of each shaft 11, 32 carries paddles 29in staggered pairs, obliquely pitched to propel the material 19 towardsthe discharge end, and, as shown in Figure 2, set obliquely to the faceof the shaft so as to slice through the material. Although both shaftsare shown identical in the pitching of the paddles, as is generallyconvenient, this is not essential; moreover, either of the scrolls mayhave paddles omitted at intervals, to reduce the local rate ofprojection by that scroll with .respect to the other scroll.

,At the feed end, the shafts ll, 12 are driven by a common gear-box 21from a reduction gear 22 driven by a motor .23, which enables the rateof rotation of the scrolls to be selected as may be required in relationto the rate of rotation of the drum. The common gear-box 21 drives theshafts l1, 12 at appropriately different speeds, the lower shaft 11,say, rotating about 50% faster than the upper shaft 12, although theupper scroll could be the one to rotate faster.

Suc-

The tips of the paddles 20 of the two scrolls rotate clear of eachother, and have a clearance from the inside of the drum shellapproximating to one-tenth of the overall diameter of each scroll. Asatisfactory arrangement for a 9 diameter drum rotated at 3 to 4 R. P.M. has two scrolls of about 2 4 diameter over the tips of the paddles,with the lower scroll rotated at 150 R. P. M. and the upper scroll at100 R. P. M. This results in the material 19 being moved forwardapproximately 3' 6" by the lower scroll for every revolution of thedrum, and approximately 2 6 by the upper scroll.

The mixing drum is particularly well suited to the mixing of iron ore,coke, flue dust, and water for sinter plants, which materials requiremore thorough incorporation than is possible with mixers of previoustypes. Thorough mixing and blending resu ts, even when the drum is fedwith each ingredient in a substantial batch, or with wide differences inthe size of the batches of successively fed ingredients.

One or more scraper blades 24 may be fitted inside the drum, to removematerial that adheres to the shell instead of cascading completely,particularly if liquids are to be introduced into the mixture, as in thecase of sinter plant mixtures, as mentioned above.

What I claim is:

l. A horizontal rotary drum mixer, comprising a rotary drum with feedingmeans at its inlet end and a discharge opening at its outlet end, atleast two paddle scrolls disposed longitudinally of the drum within theposition occupied during rotation of the drum by the material to bemixed, and each adapted to move the mixed material from the inlet to theoutlet of the drum, at least one of the scrolls having its axis offsetfrom the vertical center line of the drum in the direction of rotationof the drum, the scrolls having their peripheries spaced from the drumsurface to allow material to be moved past the tips of the paddles byfrictional contact with the drum surface to be later cascaded onto thescrolls, means for driving the drum, and means for driving the scrollsat different speeds with respect to each other in the same direction ofrotation as that of the drum to effect the movement of the mixedmaterial from inlet to outlet, the tip speed of the scrolls beingsubstantially in excess of the peripheral speed of the drum.

2. A horizontal rotary drum mixer, comprising a rotary drum with feedingmeans at its inlet end and a discharge opening at its outlet end, atleast two paddle scrolls disposed longitudinally of the drum with theiraxes at the same radial distance from the axis of the drum within theposition occupied during rotation of the drum by the material to bemixed, and each adapted to move the mixed material from the inlet to theoutlet of the drum, at least one of the scrolls having its axis offsetfrom the vertical center line of the drum in the direction of rotationof the drum, the scrolls having their peripheries spaced from the drumsurface to allow material to be moved past the tips of the paddles byfrictional contact with the drum surface to be later cascaded onto thescrolls, means for driving the drum, and means for driving the scrollsat different speeds with respect to each other in the same direction ofrotation as that of the drum to effect the movement of the mixedmaterial from inlet to outlet, the tip speed of the scrolls beingsubstantially in excess of the peripheral speed of the drum.

3. A horizontal rotary drum mixer, comprising a rotary drum with feedingmeans at its inlet end and a discharge opening at its outlet end, atleast two paddle scrolls disposed longitudinally of the drum within theposition occupied during rotation of the drum by the material to bemixed, and each adapted to move the mixed material from the inlet to theoutlet of the drum, the paddles of the two scrolls being of the sameradius, at least one of the scrolls having its axis offset from thevertical center line of the drum in the direction of rotation of thedrum, the scrolls having their peripheries spaced from the drum surfaceto allow material to be moved past the tips of the paddles by frictionalcontact with the drum surface to be later cascaded onto the scrolls,means for driving the drum, and means for driving the scrolls atdifferent speeds with respect to each other in the same direction ofrotation as that of the drum to effect the movement of the mixedmaterial from inlet to outlet, the tip speed of the scrolls beingsubstantially in excess of the peripheral speed of the drum.

4. A horizontal rotary drum mixer, comprising a rotary drum with feedingmeans at its inlet end and a discharge opening at its outlet end, twopaddle scrolls disposed longitudinally of the drum within the positionoccupied during rotation of the drum by the material to be mixed, andeach adapted to move the mixed material from the inlet to the outlet ofthe drum, one of the scroll shafts being offset from the vertical centerline of the drum in the direction of rotation of the drum and beingdisposed towards the bottom of the drum, and the other scroll shaftbeing similarly offset to a greater extent and disposed somewhat belowthe horizontal center line of the drum, the scrolls having theirperipheries spaced from the drum surface to allow material to be movedpast the tips of the paddles by frictional contact with the drum surfaceto be later cascaded onto the scrolls, means for driving the drum, andmeans for driving the scrolls at different speeds with respect to eachother in the same direction of rotation as that of the drum to effectthe movement of the mixed material from inlet to outlet, the tip speedof the scrolls being substantially in excess of the peripheral speed ofthe drum.

5. A horizontal rotary drum mixer, comprising a rotary drum with feedingmeans at its inlet end and a discharge opening at its outlet end, twopaddle scrolls disposed longitudinally of the drum with their axes atthe same radial distance from the axis of the drum within the positionoccupied during rotation of the drum by the material to be mixed, andeach adapted to move the mixed material from the inlet to the outlet ofthe drum, the paddles of the two scrolls being of the same radius, oneof the scroll shafts being oflz'set from the vertical center line of thedrum in the direction of rotation of the drum and being disposed towardsthe bottom of the drum, and the other scroll shaft being similarlyoffset to a greater extent and disposed somewhat below the horizontalcenter line of the drum, the scrolls having their peripheries spacedfrom the drum surface to allow material to be moved past the tips of thepaddles by frictional contact with the drum surface to be later cascadedonto the scrolls, means for driving the drum, and means for driving thescrolls at different speeds with respect to each other in the samedirection of rotation as that of the drum to effect the movement of themixed material from inlet to outlet, the tip speed of the scrolls beingsubstantially in excess of the peripheral speed of the drum.

References Cited in the file of this patent UNITED STATES PATENTS393,043 Twist Nov. 20, 1888 451,992 Baldwin May 12, 1891 1,980,130Fasting Nov. 6, 1934 2,570,864 Rowlson Oct. 9, 1951 2,592,334 ReiffenApr. 8, 1952

